A rubber bullet deforms momentarilly increasing the contact area (deform when contacting the wooden block) and thus reduce the impact per square area, while the aluminium bullet with the same momentum will retain its shape with the subsequent initial concentrated contact area (increasing in size as it penetrates the wooden block).
Therefore the aluminium bullet with the same diameter and momentum will also knock the block over but do an substantial amount of damage to the block than the rubber bullet.
Rubber bullet
Re: Rubber bullet
